Journal of Tea Science

Review on the Studies about Safety Assessment of Pu-erh Tea

MA Yan, CHEN Lijiao, LYU Caiyou, ZHAO Ming

Journal of Tea Science. 2018, 38(3): 221-226. doi:10.13305/j.cnki.jts.2018.03.001

Abstract ( 635 )

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Toxicology assessment is an important index to evaluate food safety. To provide scientific references for the evaluation of safety of Pu-erh tea, relative studies were reviewed. The acute oral toxicity tests showed that the LD₅₀ of Pu-erh tea was great than 5β000βmg·kg^-1, which belonged to the actual non-toxic level. The no-observed-adverse-effect-levels of non-fermented and post-fermented Pu-erh tea were 1β250βmg·kg^-1·d^-1 and 5β000βmg·kg^-1·d^-1 in 28βd or 90βd administration tests. Pu-erh tea showed no mutagenicity on the primitive, authentic and reproductive cells during genetic toxicity evaluation. The no-observed-adverse-effect level of Pu-erh tea was 700βmg·kg^-1·d^-1 for both reproductive and developmental toxicities. Little or none toxicity of Pu-erh tea to mice liver cells was observed. No pathological change was observed in human acute and subacute toxicity assays. In conclusion, the toxicology assessments proved the safety of Pu-erh tea.

Research Progress and Discussion on Fungal Contamination of Dark Tea

JIANG Yihe, XU Wei, ZHU Qi

Journal of Tea Science. 2018, 38(3): 227-236. doi:10.13305/j.cnki.jts.2018.03.002

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Microbial extracellular enzyme catalytic activity is the key factor of dark tea quality formation, and the later storage causes changes in the microbiological system in dark tea. To explore the potential food safety risks of fungus system in dark tea products, the research results of dark tea fungi pollution were reviewed. It showed that a variety of contaminating fungal toxins could be detected in dark tea samples, such as aflatoxins, ochratoxins, deoxynivalenol. Studies showed that toxin exposure of dark tea samples were low, and multi-active components of dark tea could down-regulate part of genes associating with aflatoxins, thus inhibited aflatoxin production in dark tea matrix samples. It was pointed out that it is safe to produce and drink dark tea regularly, and the development direction of dark tea processing is the application of directional fermentation technologies.

Identification of the Geographical Origins of Oolong Tea Based on EGCG, ECG and Caffeine Contents

CAO Qiong, SU Huan, WAN Xiaochun, NING Jingming

Journal of Tea Science. 2018, 38(3): 237-243. doi:10.13305/j.cnki.jts.2018.03.003

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A quantitative method to discriminate the geographical origins of Oolong teas was proposed to promote the fair of tea trade. A total of 130 Oolong tea samples were collected across China, and the chemical compositions including gallic acid, catechins, caffeine and theanine were quantified by high performance liquid chromatography. Genetic algorithm and successive projections algorithm were applied to identify important compounds, and then support vector machine, back propagation artificial neural networks and random forest models were used to classify and predict Oolong tea samples from Minnan, Minbei, Guangdong and Taiwan based on the selected compounds. The overall results indicated that compounds selected by genetic algorithm (caffeine, EGCG and ECG) combined with back propagation artificial neural networks could achieve a high efficiency in identifying Oolong tea samples from four origins, and the total identification rate in the training and prediction sets were 97.13% and 98.34%. The results provided scientific credibility to identify Oolong tea origins.

Rapid Detection of Theanine in Green Tea Based on Direct-reading Colorimetric Strips

ZHU Chengbo, WU Xiaomei, FENG Lixia, HUANG Xiangpeng, PANG Linjiang, YANG Huqing, FANG Zhengwei, WANG Ying, LAI Shuyu, ZHANG Yiming

Journal of Tea Science. 2018, 38(3): 244-252. doi:10.13305/j.cnki.jts.2018.03.004

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In this study, ninhydrin/titanium dioxide nanomaterials were constructed by using Sol-Gel method. These nanomaterial were then used as direct-reading colorimetric materials and printed on the surface loci of thin layer plate where theanine would migrate according to its retardation factor (R_f). In addition, ethanol: acetic acid developing system was chosen as developing reagent, the extraction solution of tea after being decolorized by ethyl acetate was analyzed by thin layer chromatography (TLC) via direct-reading colorimetric reaction. The results showed that the current direct-reading strip could effectively separate several amino acids in tea extraction under optimized conditions. The new constructed colorimetric nanomaterials had achieved a sensitive direct-reading coloration results for the target amino acid theanine, and the color spots on the strip were uniform and clear after self-coloration. Moreover, its color depth had a clear semi-quantitative relationship with its concentration. The current colorimetric strip has a serial of advantages including safety, easy-operation, convenient and low cost, and has a broad application prospect in fields such as quality identification of agricultural products and on-site rapid detection of amino acids.

Aroma Profiling of Tieguanyin Oolong Tea with Different Flavor Characteristics Based on Chemical Pattern Recognition

CHEN Lin, LIN Qingxia, ZHANG Yinggen, CHEN Jian, WANG Lili, YU Wenquan, YOU Zhiming

Journal of Tea Science. 2018, 38(3): 253-262. doi:10.13305/j.cnki.jts.2018.03.005

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According to the current national standards, Tieguanyin Oolong teas would be classified into three flavor types, Fresh-scent, Strong-scent and Stale-scent. In this experiment, Tieguanyin collected from their original regions (Anxi County) were categorized into several groups by preliminary sensory evaluation. Thereafter, aroma components in these tea samples were determined using headspace solid-phase micro-extraction and gas chromatography-mass spectrometry (HS-SPME/GC-MS), and their differences between new Tieguanyin (less than one year storage) with different flavor characteristics and old Tieguanyin (more than one year storage) with different storage time and quality ranks were compared through visual pattern recognition based on principal component analysis (PCA), and orthogonal partial least squares discriminant analysis (OPLS-DA) combined with other statistical methods. The results showed that aroma patterns of all tea samples could be obviously divided into two groups according to storage time. The total amount of aroma compounds was more abundant in new Tieguanyin than that of old Tieguanyin. Alcohols, esters and alkenes were the main compounds which contributed to the new fresh-scent flavor of new Tieguanyin, and aldehydes and ketones were the characteristic compounds of stale-scent flavor in old Tieguanyin. Nerolidol, indole, α-farnesene, 2-phenylethyl 2-methylbutanoate, cis-3-hexenyl hexanoate, formic acid, (2-methylphenyl) methyl ester, phenylethyl butyrate, phenylethyl isobutyrate, 2-tolylisocyanide, isopentyl hexanoate and geranyl acetone could be considered as the key markers to discriminate the two types of Tieguanyin. Moreover, new Tieguanyin could be also classified as Group 1 (Long-time withering), Group 2 (Medium-time withering and Short-time withering), and Group 3 (Strong-scent) based on their aroma constitutes. Aroma components were richer in tea samples from both Group 1 and Group 3 than those from Group 2. The acidic flavor of tea samples from Long-time withering was closely associated with ester compounds, while aroma components of tea samples from Strong-scent were mostly condensed compounds with long carbon chains. No obvious differences could be detected in old Tieguanyin, which had different storage time, but there were some potential differences among tea samples with high quality ranks. Tieguanyin of excellent sensory quality were relatively abundant in ester compounds, and low in contents of aldehydes and ketones. These results could provide references for classification, identification and quality evaluation of Tieguanyin products.

Molecular Cloning and Expression of a Cysteine Gene in Empoasca onukii

YU Yongchen, XIAO Bin, SUN Xiaoling

Journal of Tea Science. 2018, 38(3): 263-270. doi:10.13305/j.cnki.jts.2018.03.006

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Cysteine proteinases are important proteolytic enzymes for herbivorous insects. In this paper, the transcript sequence of Eocyp was obtained from the transcriptome database of Empoasca onukii. The full-length cDNA sequence of Eocyp was then cloned by RACE. The theoretical amino acid sequence of Eocyp was analyzed by bioinformatics. The expression levels of Eocyp in different developmental stages, different parts of female and male adults of E. onukii and nymphs under different temperatures and photoperiods were detected by qRT-PCR. The full-length cDNA sequence of Eocyp contained an open reading frame of 1β656βbp, which encoded 551 amino acids and had a signal peptide consisting of 24 amino acid residues. Its molecular formula was predicted to be C₂₇₈₂H₄₁₆₃N₇₃₇O₈₃₅S₂₅. Its relative molecular weight and the theoretical isoelectric point were estimated to be 62.09βkD and 6.02, and the instability coefficient of Eocyp was 36.10. Eocyp had the typical feature of cysteine protease, a catalytic triad Cys³⁵⁷-His⁴⁹⁹-Asn⁵¹⁹, and the conserved domains such as ERFNIN, GNFD amino acid residues and the GCDGG clusters. The amino acid sequence of Eocyp had a high similarity with the CYP gene of Halyomorpha halys. Expression analysis showed that Eocyp was expressed in all developmental stages of E. onukii with its peak in the fifth instar nymphs. Higher expression of Eocyp was observed in the abdomen of adult E. onukii, irrespective of female and male. However, the expression level of Eocyp did not respond to the variation of temperatures and photoperiods. These results provided a theoretical basis for further study of Eocyp.

Analysis of the Photosynthesis and Quality Components Changes in Autumn Tea

ZHANG Lan, WEI Jipeng, SHEN Chen, YAN Peng, ZHANG Liping, LI Xin, HAN Wenyan

Journal of Tea Science. 2018, 38(3): 271-280. doi:10.13305/j.cnki.jts.2018.03.007

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The time courses of different indexes, including luminous intensity in the canopy, leaf temperature, photosynthetic parameters, quality component contents and the expression of genes related to quality component biosynthesis on August 19th and September 23th were measured in Longjing 43 (Camellia sinensis cv. Longjing 43). Using the results above, the effects of luminous intensity and leaf temperature on the tea photosynthesis and the influence of luminous intensity, leaf temperature and net photosynthesis rate on the accumulation of quality components and the transcription levels of biosynthetic genes could be confirmed preliminary. The results suggested that leaf temperature and photosynthetic activity of mesophyll cells were important physiological factors to affect the net photosynthesis rate of autumn tea. Moreover, the leaf temperature might influence the biosynthesis and accumulation of catechins and amino acids in autumn tea by regulating the expression of catechins biosynthetic genes, such as CsPAL, CsF3′5′H, CsANS, CsUFGT and amino acid biosynthetic genes, including CsGS, CsGOGAT and CsTS1. Otherwise, the luminous intensity and the net photosynthesis rate of autumn tea were significantly correlated with the expression levels of genes related to catechin, amino acid and caffeine biosynthesis.

Detection and Analysis of Moisture Content in Fresh Tea Leaves Based on Hyperspectral Technology

DAI Chunxia, LIU Fang, GE Xiaofeng

Journal of Tea Science. 2018, 38(3): 281-286. doi:10.13305/j.cnki.jts.2018.03.008

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Moisture content in fresh tea leaves is an important index influencing tea quality during processing. In order to rapidly detect moisture content in tea during processing, a nondestructive method was introduced in this paper. Firstly, hyperspectral image data were captured from the fresh tea leaves. Secondly, four kinds of algorithms were used to preprocess the original data. Thirdly, the characteristic wavelength was extracted using stepwise regression analysis. Finally, a quantitative analysis model of the characteristic wavelength and moisture content in the fresh tea leaves was developed by the multiple linear regression and partial least squares regression. Experimental results showed that the best predicted effect of the partial least squares regression was obtained by the pretreatment of orthogonal signal correction after convolution smoothing and stepwise regression analysis. The correlation coefficients of the model calibration set, cross-validation set and prediction set were 0.8977, 0.8342 and 0.7749, respectively. The minimum root mean square errors were 0.0091, 0.0311 and 0.0371, respectively. Thus, hyperspectral technology could effectively detect the moisture content in fresh tea leaves, which would be useful in detecting quality changes in tea processing industry.

Research on the Behavior of Tea Consumption in China with the CKB Data

GUAN Xi, YANG Jiangfan, XIE Xiangying, LIN Chang, LI Jingyun

Journal of Tea Science. 2018, 38(3): 287-295. doi:10.13305/j.cnki.jts.2018.03.009

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Based on the 512β824 samples of 10 project areas from China Kadoorie Biobank, the tea consumption was described comprehensively and systematically. Further, the OLS model was used to analyze the factors influencing habit of tea drinking, tea-drinking frequency, daily consumption cups and consumption quantity, by dividing tea consumers into different subgroups. Results showed that household income and history of tea drinking had a significant and positive impact on tea consumers′ drinking frequency, daily consumption cups and consumption quantity. Age had a significant but negative impact on the habit of tea-drinking in China. Moreover, it had a significant and positive impact on tea-drinking frequency. The negative effects of age on daily consumption cups and consumption quantity for these heavy tea consumers were also confirmed. The results would be biased if the daily consumption cups was used in the analysis. For the future research on the tea consumption in China, this paper proposed to classify consumers and to use the daily consumption quantity in the analysis. Also, the corresponding countermeasures were put forward to expand tea consumption in future.

Quantitative Evaluation of Taste-characteristic Attributes in Three White Tea Based on Near Infrared Spectroscopy

FAN Fangyuan, YANG Mengxuan, GONG Shuying, GUO Haowei, ZHANG Kaiqi, LI Chunlin TANG Yi

Journal of Tea Science. 2018, 38(3): 296-304. doi:10.13305/j.cnki.jts.2018.03.010

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In this study, tea taste-quality evaluations and attribution analysis were performed in white teas of different producing areas, tea types and storage times. The potential of near infrared spectroscopy (NIRS) in determining taste-attributes of white tea was also evaluated. The results showed that sweet, mellow and brisk tastes were the main aspects of taste-quality evaluation in white teas. Increasing of post-oxidation degrees could significantly enhance the sweet, mellow and brisk tastes of white tea with the same leave materials and processing technology. Near infrared spectroscopy (NIRS) was used to develop four models correlating spectral data to general taste-characteristics and its individual attributes (sweet, mellow, brisk tastes and post-oxidation characteristics). The four optimized models based on near infrared spectroscopy-partial least squares (NIRS-PLS) had considerable potential for taste-quality evaluation with correlation coefficient of calibration (R_c) ranging from 0.837 to 0.987 and that of prediction (R_p) ranging from 0.748 to 0.888, which suggested that fast taste-attribute evaluation of white tea could be achieved by NIRS-PLS.

Fluorine Subcellular Distribution and Its Combining Characteristics with Cell Wall in Tea Leaves (Camellia sinensis)

LIU Siyi, ZHU Xiaojing, FANG Fengxiang, ZHANG Haojie, QIU Andong, CHEN Yuqiong*

Journal of Tea Science. 2018, 38(3): 305-312. doi:10.13305/j.cnki.jts.2018.03.011

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Tea plant (Camellia sinensis) is a hyper-accumulator of fluorine (F) and its leaves are the main accumulating tissue. In this paper, the F subcellular distribution and its binding characteristics with cell wall in tea leaves were investigated to explore the characteristics of F accumulating in tea leaves. The results showed that most of the F was distributed in the cell wall (39.74%-56.49%) and soluble fraction (28.35%-37.32%) of leaves. Pectin and hemicellulose are the main components of F enrichment and accumulated more than 90% of F in cell wall. There is a significant and positive correlation between Mn²⁺, Ca²⁺, Al³⁺ and F. The contents of F and metal elements (Mn²⁺, Fe³⁺, Ca²⁺, Mn²⁺, Al³⁺) reduced significantly in methylation and esterification cell wall while changed little in enzymolysis cell wall. These suggested that -NH₂ and -COOH might play an important role in the combination of F and cell wall, while the molecule weights of pectin and cellulose played little role. Cell wall and soluble fraction are the main sites to store F where F might be combined with -OH, -NH₂and -COOH in the form of hydrogen bonds or with metal elements in the form of ionic bonds. F might be fixed in cell wall and vacuolar as the main defense mechanism of tea plant against F toxicity.

Molecular Identification and Virulence Evaluation of an Entomopathogenic Fungus Isolated from the Cadaver of Sympiezomias citri

WANG Dingfeng, LI Liangde, LI Huiling, ZHANG Hui, WANG Qingsen, WU Guangyuan

Journal of Tea Science. 2018, 38(3): 313-318. doi:10.13305/j.cnki.jts.2018.03.012

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The taxonomic status and biocontrol potential of an entomopathogenic fungus that isolated from the cadaver of Sympiezomias citri were investigated. Amplification, sequencing, and system evolution tree construction of the nuclear ribosomal internal transcribed spacer (rDNA-ITS) and intergenic Bloc region fragments (Bloc) of the fungus Bbr4941, and the bioassay against the adult of S. citri were carried out. The results showed that the entomopathogenic fungus was identified as Beauveria brongniartii. When the adults of S. citri were dealt with Bbr4941 suspension (5.0×10⁷spore·mL^-1), the corrected accumulative mortality was 100% and LT₅₀ value was 3.916βd after 7 days. Our results showed that Bbr4941 had great potential for the biocontrol of S. citri.

Effects of Polyphenols of Old Fu Brick Tea on the Elderly Intestinal Flora

WU Genliang, HOU Aixiang, LI Ke, LI Zongjun

Journal of Tea Science. 2018, 38(3): 319-330. doi:10.13305/j.cnki.jts.2018.03.013

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To reveal the influences of tea polyphenols of old Fu brick teas on the diversity and composition of intestinal microflora in the elderly, the tea polyphenols were extracted and purified from Fu brick teas stored for 1 year and 7 years, and the isometric tea polyphenol extracts were added into the mixed medium of intestinal flora of elderly men (65 years) for the anaerobic static culture in vitro. The contents of tea polyphenols and short chain fatty acids（SCFAs）of the seven years’ tea group（O group）, one year’s tea group（N group） and the blank group（B group） were determined at 0βh, 4βh, 8βh, 12βh and 24βh. High-throughput sequencing of intestinal flora and relative bioinformatics analysis were also performed. The results showed that the polyphenols of seven years’ Fu brick tea had better effects on the increase of SCFA contents, the abundance and diversity of the intestinal flora of the elderly as compared with the control. The relative abundance of Escherichia and γ-Proteobacteria_B38 at 4βh and 12βh were significantly reduced, and the relative abundance of Bacteroides, Bifidobacterium and Faecalibacterium were also increased in O group. The above results showed that the tea polyphenol of seven years’ Fu brick tea is more beneficial to the improvement of intestinal microflora in the elderly, which was of a high potential value to the health of elderly.

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